1. Field of the Invention
This invention relates to respiratory gas delivery devices, and, more particularly, to a gas conserving device that utilizes an electronically controlled latching valve to regulate the flow of gas to a user.
2. Description of the Related Art
It is well known to deliver a flow of respiratory gas to a user in the form of supplemental oxygen. The delivery of supplemental oxygen to a patient is typically prescribed for individuals suffering from pulmonary/respiratory problems. The prescription and delivery of supplemental oxygen is undertaken to ensure that sufficient oxygen levels are being received by the patient. Situations in which supplemental oxygen may be prescribed include individual suffers from chronic obstructive pulmonary disease (COPD), asthma, diseased or damaged lungs.
The delivery of supplemental oxygen may be provided utilizing one of three predominant methods. For non-ambulatory patients, or for use during the non-ambulatory period of an individual, oxygen may be provided from a stationary oxygen concentrator that generate oxygen from air, typically using a pressure swing absorption gas separation system. While suitable for their intended purpose, oxygen concentrators are generally ill-suited for portability due the relatively bulky gas compressor and sieve beds needed to generate a practical quantity of oxygen, and, therefore, are not intended for use with an ambulatory individual.
A second predominant oxygen delivery method is a compressed oxygen system in which the oxygen to be consumed by the user is compressed and stored in a high pressure storage vessel or tank. These storage vessels can be made small enough so as to be portable. Compressed gas storage systems are generally prescribed when the user does not need oxygen all the time, such as only when walking or performing physical activity. One disadvantage of compressed oxygen systems is that oxygen is stored under pressure may create a hazard if the storage vessel is damaged, which can occur if it is dropped, bumped, punctured, etc. Also, small, portable oxygen tanks hold a relatively small amount of gas. Thus, they are limited in how long the oxygen inside the tank will last depending on the prescribed flow rate and the type/size of the tank.
A third predominant oxygen delivery method, which is typically used as an alternative to compressed oxygen systems, is a liquid oxygen (“LOX”) system. A LOX system includes a large stationary LOX storage canister that stays in the user's home. The stationary LOX canister is replenished periodically from a mobile LOX storage vessels, which is typically a truck carrying a large quantity of LOX. The LOX system also includes a small, portable delivery apparatus weighing from five to thirteen pounds that can be filled from the stationary unit for trips outside the home. The portable delivery apparatus converts the liquid oxygen to a breathable gas for consumption by the user. These systems have limited utilization due to the low LOX capacity of the portable delivery apparatus and the administered LOX flow rate. Furthermore, even when not in use, the LOX within the portable delivery apparatus evaporates at a typical rate of one pound per day, emptying the portable delivery apparatus LOX supply over time even if it is not used. Consequently, a disadvantage of a portable LOX system includes the requirement that the user must return home regularly, such as by the end of the day, to refill the portable delivery apparatus from the home stationary LOX storing canister.
A limiting factor in the utilization of compressed gas and LOX is the small quantity of oxygen stored by these respective systems. In order to ensure the portability of these systems, they tend to be as small as possible, hence limiting the oxygen capacity available for therapeutic utilization. Accordingly, to ensure that the oxygen lasts as long as possible, oxygen conserving devices are typically used in conjunction with these devices. A typical oxygen conserving device controls the delivery of oxygen such that oxygen is delivered to the user during inhalation and terminates during exhalation, i.e., upon detection of cessation of inhalation.
Oxygen conservers typically include a valve for regulating the flow of oxygen to the patient. The control of these valves may either be done electrically or pneumatically. Electrical oxygen conserving devices utilize an electric current to maintain the valve open. A traditional electrical oxygen conserving device utilizes the electric current during the entire inhalation phase of a patient. Accordingly, one of the major drawbacks of an electrical oxygen conserving device is that the power supply, namely the battery or batteries, runs down relatively quickly, necessitating frequent changing of the batteries and constant monitoring of the battery charge. For patients that are elderly or infirm, this maintenance requirement is difficult, if not impossible, and/or burdensome.
U.S. Pat. No. 5,928,189 illustrates an alternative to the traditional electrical oxygen conserving device. This patent illustrates a device including an oxygen valve having a coil that is energized with an electric pulse of a first polarity to open the valve and a subsequent electric pulse of a second polarity to close the valve. The valve is maintained in the open position by residual magnetic flux present in the magnetic circuit. The valve includes a pole piece and plunger, which are simultaneously magnetized by the electric current passing through the coil. While suitable for its intended purpose, this design has two drawbacks. First, the valve remains open only as long as there is a residual magnetic flux in the coil. Consequently, as time passes after the current is terminated, the residual magnetic flux dissipates, removing any magnetic attraction between the pole piece and plunger subjecting the valve to close due to a spring bias. Thus, the duration which the valve may be maintained in an open position is fixed depending upon the current charge provided. An additional drawback to this design is that the circuitry requires a continuous current to be supplied to the control logic, which undesirably limits the useful life of a power source.
Pneumatic oxygen conserving devices do not utilize a power source for manipulating a valve for delivering oxygen, but utilize a dual diaphragm system. A typical prior art pneumatic oxygen conserving device is disclosed in U.S. Pat. No. 6,484,721. In the device taught by this patent, a primary diaphragm controls the flow of oxygen from an oxygen source to a patient. The primary diaphragm has an open position enabling the oxygen to flow and a closed position preventing the oxygen to flow. A second, or master diaphragm, is utilized for relieving pneumatic pressure on the primary diaphragm. This is accomplished by the negative pressure caused by the patient inhaling directly or indirectly moving the slave diaphragm, which results in the pneumatic pressure being released on the primary diaphragm.
A primary drawback of a typical pneumatic oxygen conserving device is the sensitivity of the master diaphragm to an individual's inhalation pressure. If the inhalation pressure produced the patient is too small, the master diaphragm will not respond, and no oxygen will be provided to the patient during that inspiratory cycle. This situation is most likely to occur with patients having diminished respiratory effort, such an elderly patient. Likewise, there may be a time delay between the initial inhalation of the patient and the operation of the pneumatic system before oxygen is permitted to flow to the patient. These drawbacks are the result of a purely mechanical system for controlling the flow of oxygen. Furthermore, by a requiring dual diaphragm construction, multiple components are required. This results in a complex interaction of the components, which may jeopardize the reliability of the conservation device. Also, the addition components may result in a bulky and costly device. Additionally, when rating the utilization of electronic versus pneumatic controllers, electronic controllers generally provide better oxygen conservation results than pneumatic controllers.
There is a need for an oxygen conserving device that operates quickly for the delivery of oxygen to a patient and reliably. There is also a need for an oxygen conserving device that utilizes an electronic control system functioning in a way such that the longevity of its power source is extended, and provides various rates of flows of gas to the patient depending upon the patient's needs.